Don't Block "The Bat!"

A lot of spam claims (in the User-Agent or X-Mailer header) to come from a program called "The Bat!", and it may appear attractive to block this. However, this is a bad idea.

The Bat! is a legitimate email client which, like Outlook and Eudora, is often falsely impersonated by spamware. It is generally advisable for spammers to fake this header to look like a real mail client, as best they can, because it makes spam detection harder. So they do.

Spamassassin will tag and score messages that claim to be from the Bat that it can tell isn't really (just as is does for obviously false Outlook X-Mailer headers). In fact, The Bat's development team have been very helpful in this regard, providing lots of good tips on ways to tell real Bat mail from the fake stuff.